Optical system for the detection of flaws in bottles or the like

Abstract

In order to enable a laser beam to scan the complete inside surfaces of an empty bottle or the like, two mirrors oscillating about right angular axes are employed which successively reflect the laser beam. The oscillations of the two mirrors are correlated to impart an annular or spiral scanning motion to the laser beam. Subsequently passing through a converging lens, which is focused at the mouth of the bottle being tested, the laser beam enters the bottle for point-by-point scanning of its surfaces. The presence of a flaw in the bottle is sensed from the intensity of the laser beam that has penetrated, or has been reflected from, the bottle, as by an integrating sphere and a photoelectric detector mounted in position thereon. Various other embodiments of the invention and modifications are disclosed.

What is claimed is: 
     
       1. In a system for detecting flaws in bottles or like articles having a neck or constricted area near the top thereof, said system including a light beam generating means, a device for causing scanning motion of said light beam through an article to be tested, and a photoelectric detecting means adapted for detecting variation of said scanned light beam thereby to detect a flaw in the article the improvement wherein said system comprises: a laser beam generating means for generating a narrow beam of light; mirror means comprising two mirrors having respective reflective surfaces arranged so as to reflect said laser beam one after the other and supported so as to be oscillated about respective axes at right angles to each other and lying in respective planes which substantially coincide with the respective reflective surfaces for generating a scanning motion of the laser beam; means for imparting correlated oscillations to said two mirrors whereby the beam is angularly scanned in a spiral path; a positive lens for receiving said scanned beam and for redirecting it through a cross-over point or small region positioned within said bottle or article at said neck or constricted area; and, a photoelectric detector means adapted for receiving said spirally scanned laser beam after it has passed through or been reflected by said article thereby to detect a flaw in the article to be tested. 
     
     
       2. The improved system of claim 1 wherein each mirror is planar and is provided with a pair of trunnions defining the axis of oscillation of the mirror and the means for imparting said correlated oscillations to the two mirrors comprises: two closed electric circuits connected respectively to each mirror, each of said circuits including a coil part connected integrally to the respective mirror through the trunnions thereof and disposed in respective magnetic fields means for passing alternating current through each of said closed circuits, said alternating currents being 90 degrees out of phase with each other to cause correlated oscillations of the mirrors. 
     
     
       3. The improved system of claim 1 in which: each of the two mirrors is planar and is pivotally supported at one edge on a support; the means for imparting correlated oscillations to the mirrors comprises piezoelectric units, each attached to a respective one of the two mirrors and rested in a recess of said support, and means for passing alternating current through each of said piezoelectric units, said alternating currents being 90 degrees out of phase with each other. 
     
     
       4. The improved system of claim 1 wherein there is further provided a converging lens disposed between the mirror means and the article lying in a preassigned position to be tested as to the presence of flaws, said converging lens being adapted to direct the laser beam into the article by directing the laser beam at a point adjacent the mouth of the article thereby to cause scanning motion of the laser beam through the bottom and side wall of the article; and, wherein the photoelectric detecting means for receiving the scanned laser beam and sensing a flaw in the article is positioned where the laser beam, having been scanned through the article, is directed. 
     
     
       5. A flaw detecting system according to claim 4, further comprising another converging lens disposed between the laser and the optical means for collimating the laser beam. 
     
     
       6. A flaw detecting system according to claim 4, wherein the system further comprises a sheet of ground glass disposed between the bottle and the receiving and sensing means. 
     
     
       7. In a system for detecting flaws in bottles or like articles having a light beam generating means, a device for causing scanning motion of said light beam through an article to be tested, and a photoelectric detecting means adapted for detecting variation of said scanned light beam thereby to detect a flaw in the article, the improvements wherein said light beam generating means is a laser and wherein said device for causing a scanning motion includes: a lens carrier arranged for rotation about the axis of the laser beam; a lens rotatably carried by said lens carrier in an eccentric position thereon and having a radius greater than the distance between its own axis and the axis of the laser beam; means for rotating the lens carrier about the axis of the laser beam, the lens being locked against angular displacement about its own axis during the rotation of the lens carrier. 
     
     
       8. In a system for detecting flaws in bottles or like articles having a light beam generating means, a device for causing scanning motion of said light beam through an article to be tested, and a photoelectric detecting means adapted for detecting variation of said scanned light beam thereby to detect a flaw in the article the improvements wherein: (a) said light beam generating means is a laser beam generating means adapted to generate a narrow linearly-polarized laser beam; (b) said device for causing scanning motion comprises optical means disposed in the path of said polarized laser beam and adapted to move in a prescribed manner for imparting angular deflections to said beam to cause it to undergo an annular or spiral scanning motion and a positive lens for receiving said scanned laser beam and for redirecting it through a cross-over point or a small region positioned within said bottle or article and above the surface to be inspected to thereby enable said beam to scan through said article; and, (c) said photoelectric detecting means comprises means for receiving light of said laser beam which is reflected from the article, the reflected light including depolarized rays produced as a result of scattering of the polarized laser beam by a flaw of the article, means for separating the depolarized rays from the reflected light, and means for sensing the presence of the flaw in the article by receiving only the separated depolarized rays. 
     
     
       9. A system for detecting flaws in bottles or like articles, as claimed in claim 8, wherein the receiving and separating means comprises: deflecting means disposed between the optical means and the article for deflecting the light reflected from the article, said deflecting means passing the polarized laser beam travelling from the optical means toward the article; an interference filter for passing therethrough only the light that has been deflected by said deflecting means; and, a polarizing filter for passing only the depolarized rays that have passed the interference filter. 
     
     
       10. A system for detecting flaws in bottles or like articles, as claimed in claim 8, wherein a converging lens is disposed between the optical means and the article for directing the polarized laser beam at a point adjacent the open end of the article.